The dendrites of neurons are the primary surface for synaptic input in the central nervous system. To decode synaptic signals, dendrites rely on the proper transport and delivery of cell surface proteins to the dendritic plasma membrane. The goal of this proposal is to understand the cellular and molecular mechanisms that underlie the sorting and transport of endogenous neuronal proteins of physiological importance. Transmembrane proteins are sorted into carrier vesicles in the Golgi apparatus, transported along microtubules, and finally delivered to the plasma membrane. The initial step of membrane protein sorting relies on discrete amino acids in the primary sequence of the membrane protein. The experiments described within will identify new sorting signals in two dendritic G-protein coupled receptors that are relevant to neurological disorders: the D2 Long dopamine receptor and the 5HT1a serotonin receptor. We will also investigate the targeting of neuroligin, a key dendritic molecule in the composition of synapses. We will test whether or not a canonical tyrosine-based sorting signal in the molecule neuroligin is responsible for its dendritic localization, and ask if neuroligin is directly transported to the plasma membrane like other dendritic proteins characterized so far. To perform the described experiments, we will combine molecular and cellular techniques that allow for the direct observation and quantitation of the distribution of membrane proteins in neurons. By expressing wild type and mutant forms of the proteins above in low-density cultured hippocampal neurons we will compare the distribution of proteins using live-cell immunofluoresence, quantitative fluorescence microscopy, and digital image analysis. Green fluorescent protein technology will be employed to directly observe the transport of neuroligin in living neurons. Generally, neuronal polarity describes the morphological and functional differences between axons and dendrites. The establishment and maintenance of neuronal polarity is absolutely critical for nervous system function. There are several examples of human and animal diseases where the underlying cellular defect relates to problems in protein trafficking. Thus, understanding the basic aspects of protein trafficking and nerve cell biology will significantly advance our understanding of the causes of disorders like Lou Gehrig's and Alzheimer's disease.